1. Field of the Invention
This invention relates to towed sonar arrays utilized in anti-submarine warfare systems. Specifically, this invention relates to orientation detection systems used on such towed arrays.
While the present invention is described herein with reference to a particular embodiment, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings of this invention will recognize additional embodiments within the scope thereof.
2. Description of the Prior Art
Towed sonar arrays have contributed significantly to the dramatic increase in the state of the art of anti-submarine warfare technology. A towed sonar array is an array of acoustic hydrophones which are towed behind a surface ship at a predetermined depth. The hydrophones are extremely sensitive to acoustic vibration. Each hydrophone provides an electrical signal on receipt of an acoustic signal within its range of detection. An array of such detectors is capable of detecting the direction from which the acoustic signal is emanating. With computer assisted signal processing and two such arrays, a target signal may be extracted from noise and pinpointed as to location.
In order determine the exact location of the signal source, it is desirable for the orientation of the towed array to be known to within 1.degree. of arc. For this purpose, orientation detecting heading sensors have been developed. A heading sensor is essentially a compass that provides an electrical output corresponding to the orientation of the towed array relative to the earth's magnetic field. Such a sensor is produced by the Digicourse Company of Massachussets. It includes a wheel having an axis through its center and an optical coating on its surface. A magnet is mounted on the wheel to cause it to spin in response to the earth's magnetic field. An array of LED's and photodetectors is mounted above and/or below the surface of the wheel to determine its angular position.
This system was effective for early towed sonar array designs. The 2" diameter of the wheel was roughly compatible with the diameter of the hydrophone hoses assemblies. However, the new array design, referred to as the `thin-line design`, utilizes hydrophones that have a smaller outside diameter and are therefore encased in smaller protective hoses. This smaller design would permit the towing ship to travel at a higher speed without damaging the array. This would reduce the vulnerability of the towing vehicle while increasing its maneuverability. It is also anticipated that the thin-line design would be less susceptible to drift.
Unfortunately, the thin-line array design requires the heading sensor to be reduced in diameter from nearly two inches to approximately one-half an inch. Such a reduction in the outside diameter of prior art heading sensors would amount to a 15:1 decrease in wheel surface area. It is therefore believed to be virtually impossible to provide a heading sensor accurate to within 1.degree. of arc with the design.
Thus, there is a need for a heading sensor which has a diameter of less than 1 inch, preferably 1/2 an inch, and which can provide electrical signals corresponding to a compass heading accurate to within 1.degree. of arc.